1. Field of the Invention
The present invention relates to orthopaedic bone screws and more particularly to an improved orthopaedic bone screw apparatus that can be custom fitted to a patient's bone tissue by two moving parts of the bone screw apparatus that include an elongated shank and a shaped head portion that slides over the shank. More particularly, the present invention relates to an improved orthopaedic bone screw apparatus having an elongated shank and sliding head portion with a ratcheting washer that fits over the shank and enables movement in one direction toward the patient's bone tissue but disallows sliding movement in the opposite direction.
2. General Background of the Invention
During orthopaedic surgery, bone screws are often employed. Some bone screws are embedded deep into a patient's bone tissue for affixing implants to the patient's bone tissues such as intramedullary nails. The surgeon does not always know exactly the thickness of a patient's bone tissue will be such as for example of thickness of a patient's femur. Therefore, it would be desirable for the surgeon to be able to custom size a bone screw to fit a particular patient during a particular operation.
A published PCT application PCT WO98/01079 discloses a cortical bone screw assembly comprising a shaft with a threaded section and a cutting and self-tapping end section. The assembly includes a nut which includes a resilient body. The resilient body can expand to allow translational movement of he nut along the shaft, but when such radial expansion is prevented so is such translational movement. However, the nut can still be moved along the shaft by rotation on the trhead. This enables the nut to be advanced rapidly along an exposed length of shaft, but when it enters a restricted volume which prevents expansion of the resilient body, further advance can only be achieved by relative rotation.